The present invention relates to geared transmissions; more particularly, to such a transmission powered by an integral electric motor; and most particularly, to an electrically powered transmission wherein a rotary locking motor mount accurately positions and retains a motor within the transmission case without resort to any separate fasteners and also positions an idler gear shaft accurately with respect to the motor shaft.
Geared transmissions employing an electric drive motor are well known. Such transmissions are commonly used in small appliances, such as washing machines, and also, for example, in various automotive applications. These transmissions may or may not have capability for changing gear ratios (shifting) or reversing direction of rotation. Typically, a gear case is specially formed as by casting from metal or polymer for receiving a motor subassembly having a drive shaft supporting a drive gear, and an idler shaft supporting a driven gear that meshes with the drive gear to define a gear train. In some configurations, additional shafts and gears are present in the gear train to achieve specific rotary actuation purposes.
Prior art transmissions are known to be difficult and time-consuming to assemble. The drive motor must be accurately located, both axially and radially, with respect to the housing, and typically is secured to the housing via a plurality of screws or bolts. The idler shaft also must be accurately located in the housing In order to be positioned correctly with respect to the motor shaft. Normal manufacturing variation in dimensions of the housing and the motor-mounting hardware and the idler shaft-mounting hardware, as well as operator variation in placement of the motor subassembly, can result in an undesirably large variation in the distance between the motor drive axis and the idler shaft axis. Preferably, such variation is minimal so that the drive gear and driven gear have a predetermined and predictable amount of lash therebetween.
What is needed is a simple means for reliably and accurately positioning and retaining a motor subassembly and an idler shaft in a geared transmission housing without resort to threaded fasteners, gauges, or specialized assembly tools.
It is a principal object of the present invention to reduce the cost and complexity of manufacturing an electrically-powered transmission.
It is a further object of the invention to reduce the variability of interaxial spacing in such a transmission.
Briefly described, a transmission housing is formed having a well for an electric motor and a spaced-apart shaft hole for receiving an idler gear shaft. A motor is disposed in the well on spring means. The motor well is surrounded at its open end by a plurality of lugs formed in the housing and having inwardly-facing slots for receiving a motor retainer plate. The plate has a central opening for receiving and accurately positioning a shaft journal or frame extension of the motor. The retainer plate has a pattern of edge notches identical to the arrangement of the lugs but rotationally offset therefrom by an appropriate central angle. With the motor (preferably minus the drive gear) approximately centered in the well and resting on the spring means, the plate is inserted axially past the lugs via the notches, compressing the spring means, and then rotated through the central angle to engage the non-notched edge of the plate in the slots, thereby securing and positioning the motor in the well. A flange extending radially from the motor retainer plate has a second hole precisely located at a predetermined interaxial distance from the plate center hole. With the plate rotated into motor-retaining position, the second hole is coaxial with the shaft hole in the housing. An idler shaft pressed into the second plate hole and the shaft hole in the housing is thus properly positioned with respect to the motor drive shaft and further locks the retaining plate against rotating backwards from engagement with the lugs.